The present invention relates to apparatus and methods for monitoring the operation of rotating machines, such as compressors and pumps in heating, ventilation and air conditioning systems; and more particularly to apparatus which monitors vibration of such rotating machines.
Rotating machines have a wide variety of applications. For example, motors drive compressors and pumps in heating, ventilation and air conditioning (HVAC) systems found in most buildings. Inevitably such machinery develops various mechanical problems with time. Bearings wear, cracks and other deformations develop, and the rotating components become unbalanced. Initially such faults merely reduce the efficiency and performance of the machine. However, if not remedied in time, the faults can progress in magnitude to a point at which the machine fails to operate or cause damage to other components. A relatively inexpensive and simple repair if made early in the fault progression can prevent more serious and expensive subsequent repairs.
Therefore, it is desirable to detect and locate malfunctioning components as early as possible. Furthermore, it is desirable to detect such faults without interfering with normal machine operation. Taking a machine out of service to perform diagnostic operations may be undesirable and inefficient. Furthermore, the onset of many defects often is not apparent without extensively dismantling the machine.
It is known that many defects in a rotating machine generate periodic vibrations that are discernibly different from vibrations produced when that machine is properly operating. Most vibration based diagnostic work has been done by experienced engineers based on their empirical knowledge. However, it is desirable to enable less experienced technicians to service machinery. Therefore it is further desirable to provide equipment which analyze the vibrations and provide indications of the occurrence of a fault and the component that is failing.
Heretofore, equipment that automatically diagnoses faults had to be developed for a particular rotating machine. Many characteristics of a machine""s design contribute to vibrations which occur during normal operation and the manner in which the vibrations change during various fault conditions. This required that a separate computer program be written to analyze the vibration signals for a specific machine configuration. Thus if a particular machine configuration is not in a repertoire of analysis programs, new analysis software must be developed. Because new types of rotating machines are constantly being developed, it is impractical to develop analysis software for every machine using conventional techniques.
As a consequence, if the design of the machine changed or components were replaced with ones that were not the same as the original components, the vibration patterns during fault-free and fault operation could change. For example, the vibration pattern of the entire machine might change significantly if a repair is made using a different type of motor. In that case, the equipment that analyzed vibrations to detect faults also had to be modified which could require extensive engineering analysis and software development. Such modification of the fault diagnostic equipment is not economically justified unless a relatively large number of machines are altered in the same manner.
Faults occurring in a rotating machine are diagnosed by a method which configures a diagnostic apparatus by storing a definition of the particular rotating machine. That definition specifies components and their functional characteristics. In the preferred embodiment of the method, the rotating machine is defined by storing a table of components and modifying that table with data specifying operational characteristics of each component. In that embodiment, the definition of the rotating machine also may incorporate site specific features that are unique to the particular installation of the machine. The configuration of the rotating machine further includes identification of sensors which provide operational data related to the rotating machine""s performance. For example, such operation data may be related to machine vibration, oil contamination, or refrigerant analysis.
The diagnostic procedure is defined by storing specification of portions of the operational data from the sensors which are to be selected for analysis. Analytical rules are provided which specify formulae by which machine faults are deduced from the portions of the operational data. For example, the analytical rules may be stated as signature rules and problem rules. The signature rules define formulae by which machine performance characteristics are deduced from the portions of the operational data. The problem rules define formulae by which machine faults are deduced from the machine signatures. Both types of rules may utilize the site specific definition of the rotating machine to customize the analysis to that particular machine.
The analysis of the rotating machine""s operation is performed by acquiring actual operational data from the plurality of sensors. The specifications are employed to extract portions of the actual operational data which are to be operated on by the rules to detect faults in the rotating machine. In response to this process an indication is generated when a fault is detected. In the preferred embodiment, salient observations about the machine operation are extracted from the operational data. These observations include, for example, peak amplitudes and their corresponding frequencies from a set of vibration measurements. Signature rules then are applied to the salient observations to deduce the signatures of the machine. Such signatures may include harmonics that are present for the machine. Then problem rules are applied to the signatures to deduce when faults occur.
The present method enables the analytical process to be configured to different type of rotating machines and reconfigured when functional characteristics of a given machine change, such as upon replacement of a component.